JPS6217018B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a copper alloy for welded pipes having excellent corrosion resistance and weld cracking resistance in welded parts. In recent years, thin-walled copper alloy pipes have come to be welded by high-frequency resistance welding or high-frequency induction welding. This tendency is particularly noticeable for tubes used in radiators. Conventionally, lock seam tubes have been used for radiators, but due to the demand for cost reduction and increased production efficiency, welded tubes made by high-frequency resistance welding or high-frequency induction welding are increasingly being adopted. However, copper alloy welded pipes have the disadvantage that the welded portion has significantly lower corrosion resistance than other parts due to the uniqueness of its welded structure. Considering the deterioration of the usage environment in recent years, this is a major restriction on the use of copper alloy welded pipes. Furthermore, when high frequency induction welding or high frequency resistance welding is used as a welding method when manufacturing copper alloy welded pipes,
Due to the characteristics of its welding method, it has a manufacturing difficulty in that it is particularly prone to weld cracking. Under these circumstances, there is a demand for materials that have excellent corrosion resistance in welded areas and have low weld cracking susceptibility. The present invention was developed as a result of research conducted in view of the above situation.Zinc 25-40wt% (hereinafter all alloying elements are referred to as wt%), phosphorus 0.005-0.070%, tin
0.05 to 1.0%, the balance being copper and unavoidable impurities, and the grain size is 0.015 mm or less (the grain size in the present invention means the grain size after final annealing), which improves corrosion resistance and resists weld cracking. We have developed a copper alloy for welded pipes with improved properties. Regarding the alloy components in the copper alloy for welded pipes of the present invention, their effects, addition amounts, and reasons for limiting the crystal grain size will be explained. Copper and zinc are the basic materials of the alloy of the present invention, and have excellent workability and mechanical strength, as well as excellent thermal conductivity. The reason why the amount of zinc added is limited to the above range is that if the zinc content is less than 25%, the workability will deteriorate, and if the zinc content exceeds 40%, precipitation of β phase will be observed in the copper-zinc alloy, resulting in poor corrosion resistance and cold workability. This is because workability deteriorates. The amount of phosphorus added
The reason for setting it to 0.005 to 0.070% is that the amount of phosphorus added is
This is because if it is less than 0.005%, no improvement in the corrosion resistance of the welded part is observed, and if it exceeds 0.070%, although the corrosion resistance is improved, signs of intergranular corrosion are observed. The reason why the amount of tin added is 0.05 to 1.0% is that if the amount of tin added is less than 0.05%, no improvement in the corrosion resistance of the welded part will be observed, and if it exceeds 1.0%, the effect of improving corrosion resistance will be saturated. This is to do so. Furthermore, the reason why the crystal grain size was limited to 0.015 mm or less will be explained. As a result of investigating the causes of weld cracking caused by high-frequency induction welding or high-frequency resistance welding, the present inventors found that grain boundaries become brittle when in contact with molten base metal, and weld cracks occur when subjected to a light impact. We found that this occurs. As a result of conducting various investigations into such phenomena, it was found that the influence of the crystal grain size is large, and that by reducing the crystal grain size, the sensitivity to such phenomena is significantly reduced. The reason why the grain size is limited to 0.015 mm or less is that if the grain size exceeds 0.015 mm, weld cracking is likely to occur. Examples Alloys having the compositions shown in Table 1 were melted and hot rolled at 700°C to form a plate with a thickness of 8 mm, which was then cold rolled to a thickness of 3 mm. This was annealed at 500°C for 1 hour, and then finally cold rolled into a plate with a thickness of 1 mm. This was further heat-treated at various temperatures of 350 to 600°C for 1 hr, and the crystal grain size was adjusted to the size shown in Table 1, and then used for testing. The welded parts to be subjected to the corrosion resistance test were manufactured by butting together 1 mm thick alloys having the compositions shown in Table 1 and performing TIG welding. Corrosion resistance test was conducted by dissolving 1.3 g of sodium bicarbonate, 1.5 g of sodium sulfate, and 1.6 g of sodium chloride in 1 water, maintaining the liquid temperature at 88°C, and heating at 100 m/min.
ml of air was blown into it, and it was immersed in this solution for 240 hours. The depth of dezincification corrosion that occurred at that time was measured for the welded part, and the corrosion resistance was evaluated based on this. The results are shown in Table 2. A test for resistance to weld cracking caused by embrittlement of grain boundaries when in contact with molten base metal was carried out using 1 mm thick alloys with various compositions shown in Table 1 in a pipe shape as shown in Figure 1. It is immersed for 3 seconds in molten metal of the same composition maintained at +50°C, melting point, and then taken out and shocked in a holding furnace with the attached metal melted as shown in Figure 2. added. The cross section of the deformed pipe was then observed under a microscope to confirm the presence or absence of intergranular fracture, and this was used to evaluate resistance to weld cracking. The results are shown in Table 3. In other words, the maximum dezincification corrosion depth in the welds for the comparative alloys (sample numbers 1 to 5) is 270 to 364μ, while the maximum dezincification corrosion depth in the welds for the invention alloys (sample numbers 6 to 13) is 270 to 364μ. It is found that the dezincing corrosion resistance of the alloy of the present invention is extremely excellent. In addition, although the present invention alloy has excellent dezincification corrosion resistance as described above, in addition, those with a grain size of 0.015 mm or less (sample numbers 6 to 13) simply undergo ductile deformation in the weld cracking test shown in Figure 2. Weld cracking resistance is improved with no cracking. On the other hand, crystal grains with a grain size exceeding 0.015 mm are not preferred because they cause grain boundary fracture. Therefore, the crystal grain size is adjusted as appropriate depending on the use of the pipe. As described above, the alloy of the present invention has extremely excellent properties as a copper alloy for welded pipes.

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【table】 [Brief explanation of the drawing]

Figure 1 shows the thickness of 1mm used in the weld cracking resistance test.
FIG. 2 is a cross-sectional view of the alloy pipe shown in FIG. 1: 1mm thick alloy pipe (10mm length), 2:
Free falling object (weight 200 gw), 3: Support stand, 4: Heating and holding furnace, a: Pipe inner diameter (φ20 mm), b: Pipe outer diameter (φ22 mm), c: Falling distance of falling object 2 (50
mm).

Claims (1)

[Claims] 1 Zinc 25-40wt%, phosphorus 0.005-0.070wt%, tin
A copper alloy for welded pipes, consisting of 0.05 to 1.0 wt%, the balance being copper and unavoidable impurities, and having a crystal grain size of 0.015 mm or less.